The present invention relates to pavement marking materials which may be adhered to a roadway surface to provide traffic control marking. It also relates to adhesive layers useful in adhering pavement marking material to a roadway surface.
Pavement markings convey information to drivers and pedestrians by providing exposed visible and/or reflective surfaces which serve as indicia upon a roadway surface. In the past such a function was typically accomplished by painting portions of a roadway surface. Modern pavement marking materials offer significant advantages over paint such as dramatically increased visibility and/or reflectance, improved durability, and temporary removable marking options. Two examples of modern pavement marking materials are pavement marking sheet materials and raised pavement markers.
Continuous and skip lane stripings on highways and pedestrian crosswalk markings employ preformed pavement marking sheeting preferably comprising a wear-resistant top layer optionally overlying a flexible base sheet. The top layer is generally highly visible, may include reflective elements to enhance detection when illuminated by traffic at night, and serves as indicia when installed upon the roadway surface. Application of pavement marking sheeting to a roadway surface has typically been by contact cement or rubber-based pressure-sensitive adhesives.
Another example of a pavement marking is a raised pavement marker (i.e. a discreet marking structure with a rigid, semi-rigid or flexible marking body) which when applied to a roadway surface provides a raised surface. Often, the raised surface is both reflective and strategically oriented to enhance reflective efficiency when illuminated by traffic at night. In the case of rigid discreet markers, attachment of the body of each marker to the pavement surface has involved hot-melt adhesives or epoxy systems. Flexible body raised pavement markers have also been attached to pavement surfaces or pavement marking sheeting by soft butyl mastic materials.
In order to fulfill their function as indicia, both raised pavement markers and pavement marking sheeting must be applied to a rather troublesome substrate. That substrate, the roadway surface, varies widely in terms of surface properties because the underlying material may be concrete or asphalt, may be of varying age and temperature, and may, on occasion, be moist or damp or oily. Additionally, the roadway surface may vary in texture from rough to smooth. The substrate surface properties, therefore, represent a considerable challenge for adhesive attachment.
Some of the deficiencies associated with present pavement marking adhesives include: (1) inability to be applied due to limited adhesive tack at low temperature; (2) limited ability to accommodate surface roughness; (3) reduced durability, particularly at low temperature, when subjected to impact or shear; (4) increasing adhesion over time which in turn limits the duration of a period during which a temporary installation may be efficiently removed; and (5) staining of light colored concrete roadway surfaces by adhesives in removable markers. Additionally, particularly in the case of rigid body raised pavement markers, a rigid adhesive attachment to the pavement surface increases the susceptibility of the body of the marker to shattering upon impact by a vehicle tire. Further, inability of the adhesive to bridge gaps between a rigid raised pavement marker and a rough road surface may lead to early detachment of the marker from the roadway surface.
The practical significance of such deficiencies in adhesive systems is a tendency towards either inadequate initial bonding (i.e. through insufficient adhesive tack) or inadequate permanent bonding of a marking sheet to the roadway surface. Some pavement marking sheets have a somewhat elastic nature and their slow but progressive tendency toward recovery after initial application may exceed adhesive forces bonding the sheet to the pavement and result in the pavement marking sheet becoming detached. Once the pavement marking sheet becomes prematurely detached from a roadway surface, advantages such as more effective visibility and potentially longer service life cannot be realized. Similarly, a shattered or detached raised pavement marker will fail to serve in its intended function as an indicium. Further, inadequate adhesive tack at low temperature limits the application season in many locations which in turn leads to less efficiently marked highway projects.
In view of the above-described deficiencies associated with adhesion of pavement marking sheets or raised pavement markers to roadway surfaces, a desirable adhesive system would embody the following properties:
1. Extended temperature range for application. PA1 2. Durability of application/adhesion. PA1 3. Acceptable cost. PA1 4. Efficient installation. PA1 1. Peel force does not drastically increase over time. PA1 2. Non-staining to concrete pavement. PA1 1. Accommodates irregularities between the pavement surface and the rigid body of a raised pavement marker. PA1 2. Protects or cushions a raised pavement marker from the shock of impact from a vehicle tire.
Additionally, if the system is to be removable from the pavement, an adhesive system would desirably embody the following properties:
Additionally, in the case of rigid body raised pavement markers, an adhesive system would desirably embody the following properties:
The present invention, as disclosed below, satisfies these requirements with silicone pressure-sensitive adhesive systems which are highly useful for pavement marking tapes and raised pavement markers.